1. Field of the Invention
The present invention relates to a stepping motor structured by a rotor constituted by a permanent magnet and a stator around which an exciting coil is wound, and more particularly to a lead screw type stepping motor in which a rotation of the rotor is converted into a linear movement by a slider to output toward an outer portion.
2. Description of Conventional Art
A conventional lead screw type stepping motor is shown in FIGS. 2 and 3. FIG. 2 is a vertical cross sectional side view, and FIG. 3 is a vertical cross sectional side view in a line Xxe2x80x94X in FIG. 2. Reference numeral 10 denotes a stator around which an exciting coil 11 is wound. A rotor 13 provided with a permanent magnet 12 is arranged inside of the stator 10. The rotor 12 is rotatably supported to the case 14 receiving the stator 10, a left end of the stator 10 is rotatably supported to a first support member 15 by a first bearing 16, and the right end of the stator 10 is rotatably supported to a second support member 17 by a second bearing 18. Further, a female threaded hole 19 is pierced through in the center of the rotor 13 along the longitudinal direction Axe2x80x94A. Further, a rod-shaped slider 20 is engaged with the female threaded hole 19 of the rotor 13, the right end of the slider 20 protrudes outward and a rotation of the slider 20 is inhibited by the following manner. An oval-shaped segmental circle portion 20A is provided near the right end of the slider 20, and this segmental circle portion 20A is arranged to and guided by an oval-shaped segmental circle hole 21B formed in a bottom portion 21A of a cup member 21 which is fixedly arranged in the right end of the case 14. The segmental circle portion 20A and the segmental circle hole 21A are disclosed in FIG. 3.
In accordance with the structure mentioned above, when a pulse signal for control is input to the exciting coil 11, the rotor 13 rotates one step angle by one step angle every one pulse input, and the rotor 13 rotates in correspondence to the input signal. Further, in accordance with the rotation of the rotor 13, since the rotation of the slider 20 is inhibited by the segmental circle portion 20A and the segmental circle hole 21B, the slider 20 moves linearly in the axial direction of the slider 20 in correspondence to the rotation of the rotor 13. On the other hand, a movement of the slider 20 to the right side in FIG. 2 is regulated by a right end portion 22A of a male screw 22 being brought into contact with the bottom portion 21A of the cup member 21.
In accordance with the conventional lead screw type stepping motor, since cross sectional shapes of the segmental circle portion 20A formed in the slider 20 and the segmental circle hole 21B formed in the cup member 21 are formed in an oval shape, it is hard to form a flat portion with an accurate symmetry level and an accurate shape precision, and there is a risk that non-reaction area is generated at a time when the rotor 13 rotates and reversely rotates. Particularly, in the case that this non-reaction area is great, there is a risk that a dicrepancy is generated between a number of pulse input to the stepping motor and a moving amount of the slider 20. In accordance with the structure mentioned above, it is impossible to provide a lead screw type stepping motor having a high response and controllability with respect to the input signal applied to the motor. Further, in FIG. 2, the regulation of the rightward movement of the slider 20 is achieved by bringing the right end portion 22A of the male screw 22 into contact with the bottom portion 21A of the cup member 21, however, in accordance with this structure, there is a risk that a regulated position is changed by a displacement of an assembled position at a time of assembling the cup member 21 in a right side plate 14A of the case 14, so that it is impossible to carry out an accurate initial alignment of the stepping motor.
The present invention is made by taking the problems mentioned above into consideration, and an object of the present invention is to provide a lead screw type stepping motor which is excellent in a response and a controllability with respect to an input signal applied to the motor, and can carry out an accurate initial alignment.
In accordance with the present invention, in order to achieve the object mentioned above, there is provided a lead screw type stepping motor structured such that a rotor is rotatably supported inside a stator around which an exciting coil is wound, a slider is arranged to be screwed with a female threaded hole provided through in a longitudinal direction of the rotor, and a rotation of the rotor is converted into a linear movement of the slider to be output, wherein a slit groove shaped in an oblong hole along the axial direction is pierced through in the slider, the slider is supported to a guide hole provided in a bearing portion of a case receiving the stator in such a manner as to freely move in the axial direction, a guide pin is arranged to be inserted into the slit groove, and both ends of the guide pin are press inserted and supported to the bearing portion.
When a pulse signal is input to the exciting coil and the rotor rotates, the slider which is inhibited by the slit groove and the guide pin from rotating, linearly moves in the axial direction of the slider. The slider rotation inhibiting means is achieved by the slit groove and the guide pin, and it is possible to maintain accuracy of manufacturing the slit groove and the guide pin, whereby it is possible to largely improve a response and a controllability of the slider with respect to the input signal applied to the motor. Further, since moving amount to one side and another side in the slider are regulated only by a length of the slit groove and the guide pin, it is particularly possible to accurately regulate the moving amount to one side and another side in the slider.